1. Field of the Invention
The present invention relates to a method of linking a piston rod to various compressor components.
2. Description of the Related Art
In general, wobble type compressors compress gas by converting the wobbling motion of a swash plate into the reciprocal motion of a piston inside a cylinder. The usual wobble type compressor thus utilizes a rotating drive shaft to support a swash plate that wobble as the drive shaft revolves. The piston is linked to the swash plate via a piston rod, and the piston performs a reciprocating operation as the swash plate wobbles.
In order to convert the wobbling movement of the swash plate into a reciprocating operation of the piston, the piston rod must be linked to the swash plate and piston in such a way that permits the oscillatory movement of the swash plate, piston rod and piston. Accordingly, as shown in FIG. 7, a piston rod 12 is provided with balls 120 and 121 integrally formed at each end of the piston rod. A cavity 13, defined in the swash plate 10, has a shape that conforms to that of the ball 120. Another cavity 14, having a shape conforming to that of the ball 121, is defined in a piston 11.
The cavities 13 and 14 receive and supports the balls 120 and 121, respectively, in such a way that the balls 120 and 121 are slidable along the inner wall surface of the cavities 13 and 14. A pair of cylindrical walls 21 extend from the opening edges of the cavities 13 and 14 and are caulked at portions defined by the circumferences of the balls 120 and 121. This permits the balls 120 and 121 to be slidably retained along the inner wall surfaces of cavities 13 and 14. The balls 120 and 121, thus secured in the cavities 13 and 14 link the swash plate 10, piston 11 and piston rod 12 together and permit their oscillatory movement.
The assembly of the ball 120 and swash plate 10 requires that the ball 120 be fitted or incorporated to the swash plate 10. This is commonly done by first providing a cylindrical wall 21 which has a uniform thickness formed along the opening edge of the cavity 13, as shown in FIG. 8. A punch 20 having a bowl surface 200 is then pressed against the cylindrical wall 21 to plastically deform the cylindrical wall 21 along the circumference of the ball 120 placed in the cavity 13, as shown in FIGS. 8 and 9. The ball 120 is in this way made an integral component with the swash plate 10. The same process is used to link or integrate the piston rod 12 with the piston 11. After incorporation of the piston rod 12 into the swash plate 10 and piston 11, the punch 20 is then split at the parting line 201 and retracted from it's previous position.
Should the height of the cylindrical wall 21 be increased in order to enhance the wall's strength, the area of contact between the inner circumferential surface of the cylindrical wall 21 and the ball 120 or (121) would likewise increase. Increasing this area of contact, however, inhibits the smooth oscillation of the rod 12 with the balls 120, 121. It follows from this that increasing the height of cylindrical wall 21, promotes energy loss and a decrease to the overall operational efficiency of compressor.
In addition, utilizing a large area of contact between the cylindrical wall 121 and ball 120 prevents adequate lubrication from being supplied to the contact area. This makes burning likely to occur between the cylinder wall 21 and ball 120. A further disadvantage of increasing the height of the cylindrical wall 21, is the manufacturing difficulties presented in linking the piston rod 12 to ball 120 etc. By increasing the height of the cylindrical wall 21, a greater plastic deformation is required during the assembly and linkage of the cylindrical wall 21 to the ball 120. This tends to lower the durability of the cylindrical wall 21 by increasing the concentration of internal stresses at the cylindrical wall's root.